For information on the plethora of known oxo bridged tetranuclear manganese compounds, reference is made to the following review articles: K. Wieghardt, Angew. Chem. Int. Ed. English, 28, p. 1153 (1989); J. B. Vincent, G. Christou, Adv. Inorg. Chem., 33, p. 197 (1989); G. Christou, Acc. Chem. Res., 22, p. 328 (1989); and G. W. Brudvig, R. H. Crabtree, Prog. Inorg. Chem.. 37, p. 99 (1989). As can be deduced from these articles, the manganese in these compounds appear in various oxidation states, spatial arrangements and the like. Importantly, none of the compounds reported have the unique core of the novel compounds of the present invention.
More recently, a sodium salt of a valence delocalized oxo bridged tetranuclear manganese compound was reported by W. H. Armstrong et al at the 199th ACS National Meeting. A portion of that report is included in the printed abstracts of the meeting. (See Abstract of Papers, Part 1, 199th ACS National Meeting, Apr. 22-27, 1990, Abstract No. 397.) Importantly, the compounds of the present invention are distinguishable from the compounds reported at that meeting.